The present invention relates generally to a technique including a process and resulting structure for a copolymer resin for an ultra-shortwave light source such as KrF or ArF. More specifically, it relates to a copolymer resin, where a norbonyl(meth)acrylate unit is introduced to a copolymeric structure for a photo resist. The photo resist can be used in a variety of lithography processes using a KrF (248 nm) or ArF (193) light source which is a light source to be applied in next generation memory elements such as 1G or 4G DRAM integrated circuit chips.
In general, characteristics such as etching resistance, adhesiveness with low light absorption at 193 nm wavelength are often desired for a copolymer resin for ArF. The copolymer resin should also be developable by using, for example, a 2.38 wt % aqueous solution of tetramethylammonium hydroxide (TMAH). It is difficult, however, to synthesize a copolymer resin satisfying some or all these desirable characteristics. Many researches have often focused on studies on a norbolac type resin as a material to increase transparency at 193 nm wavelength and increase etching resistance. Thus, attempts to employ(meth)acrylate resins having high transparency, and to introduce alicyclic compounds to resin side chains in order to overcome limitations of deficient etching resistance, have been suggested. For example, IBM suggested the use of a copolymer resin represented by following chemical formula I: ##STR1##
where R.sub.1, R.sub.2 and R.sub.3 independently represent hydrogen or methyl.
The copolymer resin represented by chemical formula I unfortunately has increased hydrophobicity. The increased hydrophobicity occurs, in part, from introducing an alicyclic compound to the side chain, which decreases solubility in the developing solution and weakens adhesiveness, so that the compound can be contained in the copolymer resin composition in an amount not more than a certain level. It should be noted that if the alicyclic compound is included at less than the certain level, satisfactory etching resistance cannot generally be achieved. It has been found that, among the conventional alicyclic groups on side chains, which are commonly known, the norbonyl or admantyl group is effective in view of etching resistance. The conventional copolymer resin including formula I has a severe limitation in that adhesive strength decreases by gaining hydrophobicity as the content of the cyclic compound in the resin composition increases.
From the above, it is seen that an improved photo resist that has improved characteristics is highly desirable.